In Patent document 1, the dual mode communication method has been disclosed in which a terminal selectively connectable to multiple communication systems switches the communication system to which the terminal should set up a connection. In the technology disclosed in the Patent document 1, when the terminal that is communicating via a W-CDMA system has detected that the residual battery has decreased to less than a predetermined threshold, the terminal determines whether or not it possible to communicate by using a GSM system which can operate with power consumption less than that of the W-CDMA system, and a connection of the terminal and the W-CDMA system is switched into a connection of the terminal and the GSM system without the communication via the W-CDMA system disconnected if it is determined possible to communicate with the GSM system.
Besides, in recent years, a combined wireless terminal device connectable to a network as well such as a wireless LAN network that is narrow in a cell range but is capable of making high-rate communication, in addition to a wireless communication network such as a 3G network that is slow in communication but is wide in a cell range, and connectable in any place, has made its appearance.
One example of the wireless base station device and the wireless terminal device of this type, which have been conventionally developed, is described in Patent document 2. These devices are employed for a purpose of easily realizing an inter-system handover scheme without increasing a load imposed upon the wireless terminal device. This technology is configured of a combined wireless terminal device and base station devices for a plurality of networks. The system having this configuration operates as follows. The base station device of a 3G wireless communication network acquires periodically position registration information of the base station device of the wireless LAN network. Further, the terminal device acquires position information of the wireless LAN base station device from the 3G communication network base station device, and acquires a bandwidth occupation situation of a wireless channel within a cell of the above wireless LAN base station with a scan by the wireless LAN communication.
Patent document 1: JP-P2006-279577A
Patent document 2: JP-P2005-086471A